(1) Field of the Invention
The present invention relates to an unsaturated bismaleimide compound type thermosetting resin composition. More particularly, the present invention relates to a thermosetting liquid resin composition which is excellent in not only heat resistance and strength but also flame retardancy and light weight characteristic.
(2) Description of the Prior Art
A thermoset product of an unsaturated bismaleimide compound obtained by reacting an amine with maleic anhydride has an excellent heat resistance, and moreover, since the curing polymerization reaction is an addition reaction, no volatile component is formed at the curing step and a dense cured product is advantageously obtained. However, since the unsaturated bismaleimide compound is poor in the solubility in an ordinary organic solvent, a high-boiling-point solvent having a high polarity, such as dimethylformamide or N-methylpyrrolidone, should be used for formation of a solution of this compound. As means for improving this low solubility, there has been adopted a method in which the unsaturated bismaleimide compound is modified by incorporation of, for example, an epoxy resin, but this method is defective in that a precipitate is formed at room temperature or the viscosity becomes too high. Accordingly, a thermosetting resin composition of this type can hardly be used in the form of a solvent-free composition.
Under this background, we previously proposed an unsaturated bismaleimide compound type thermosetting resin composition which can be used in the form of a solvent-free composition (Japanese Patent Application Laid-Open Specification No. Sho 61-272227).
This resin composition comprises (a) a preliminary reaction product between a polyamino compound and an unsaturated bismaleimide compound, (b) an epoxy group-containing vinyl compound, (c) an epoxy curing agent and (d) a radical polymerization initiator as indispensable components.
The above-mentioned composition according to the prior art is sufficiently satisfactory in such characteristics as heat resistance and strength, but is still insufficient in flame retardancy, light weight characteristic and the like.
At the present, development of a molding material which is excellent in not only such characteristics as heat resistance and strength but also flame retardancy and light weight characteristic is especially desired mainly in the fields of aerial navigation and space development. The above-mentioned composition fails to satisfy this requirement.